Shillingburg HT, Hobo S, Jacobi R, Brackett SE, 3rd edn. Chicago: Quintessence Pub Co Inc; 1997
Ibbetson R Clinical considerations for adhesive bridgework. Dent Update. 2004; 31:254-265
Dahl BL, Krogstad O, Karlsson K An alternative treatment in cases with advanced localised attrition. J Oral Rehab. 1973; 2:209-214
Dahl BL, Krogstad O Long term observations of an increased occlusal face height obtained by a combined orthodontic/prosthetic approach. J Oral Rehab. 1985; 13:173-178
Ozer F, Unlu N, Sengun A The influence of dentinal regions on bond strengths of different adhesive systems. J Oral Rehabil. 2003; 30:659-663
Buonocore MG A simple method of increasing the adhesion of acrylic filling materials to enamel surfaces. J Dent Res. 1955; 34:(6)849-853
Saad AA, Byrne D, Hussey D Effects of groove placement on retention/resistance of maxillary anterior resin-bonded retainers. J Prosthet Dent. 1995; 74:133-139
Djemal S, Setchell D, King P, Wickens J Long term survival characteristics of 832 resin-retained bridges and splints provided in a post-graduate teaching hospital between 1978–1993. J Oral Rehabil. 1999; 26:302-330
Olsen RA, Duke S, Norling BK Enamel reduction and the bond strength of resin bonded retainers. J Prosthet Dent. 1988; 60:32-35
Shillingburg Jr HT, Jacobi R, Bruckett SEChicago: Quintessence Publishing Co Inc; 1987
Smith BGN, 3rd edn. London: Martin Dunitz Ltd; 2000
El Salam Shakal MA, Pfeiffer P, Hilgers RD Effect of tooth preparation on bond strengths of resin-bonded prostheses: a pilot study. J Prosthet Dent. 1997; 77:243-249
Aker DA, Aker JR, Sorensen SE The effect of methods of enamel preparation on the retentive strength of acid-etch composite resins. JADA. 1979; 99:185-189
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Creugers NHJ, Kayser AF, Van't Hof MA A seven and a half survival study of resin-bonded bridges. J Dent Res. 1992; 71:(11)1822-1825
Boening KW, Ullmann K A retrospective study of the clinical performance of porcelain-fused-to-metal resin-bonded fixed partial dentures. Int J Prosthod. 2012; 25:265-269
Pjeterssun BE, Tan WC, Tan K, Bragger U, Zwahlen M, Lang NP A systematic review of the survival and complication rates of resin-bonded bridges after an observation period of at least 5 years. Clin Oral Implantol Res. 2008; 19:131-141
King PA, Foster LV, Yates RJ, Newcombe RG, Garrett MJ Survival characteristics of 771 resin-retained bridges provided at a UK dental teaching hospital. Br Dent J. 2015; 218:423-428
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Controversy exists surrounding resin-bonded bridges (RBBs), particularly with regards to abutment preparation. Should the abutments be prepared? If the abutments are prepared what design should be adopted? If there is to be no preparation, will there be space for the restoration? Many factors need consideration when planning for this treatment. This article aims to explore the effect of abutment preparation. In this regard, a literature review was conducted to present the latest available evidence.
CPD/Clinical Relevance: Minimal intervention is key in modern dentistry, so clinicians must be able to make confident decisions in the provision of minimally invasive treatments like the RBB and be aware of the latest evidence.
Article
Two schools of thought exist within this field; one which advocates abutment tooth preparation and one which believes that preparation is unnecessary.
In 1997, Shillingburg stated that ‘no cements compatible with living tooth structure and the biologic environment of the oral cavity possess adequate adhesion properties to hold a restoration in place solely through adhesion’.1 It stands to reason, therefore, that some degree of tooth preparation is necessary to afford the resin-bonded bridge (RBB) retention form and resistance. But how accurate is Shillingburg's statement and is there any evidence for it?
Conversely, Ibbetson2 stated that an RBB cemented onto unprepared enamel will enjoy a satisfactory longevity without having to compromise the integrity of the abutment. This ideology relies upon the Dahl principle, whereby space for the restoration is gained through axial tooth movement in place of tooth reduction.3,4
History
Acid etch technology
In 1955, Michael Buonocore discovered the acid-etch technique which facilitated bonding to enamel.5,6 This innovation led to the emergence of minimally invasive dentistry using resin-based materials, and hence the RBB some decades later.7,8
Resin-bonding
Alain Rochette initiated the concept of the RBB in the 70s.9 He utilized the technique primarily for splinting mobile mandibular anterior teeth. The original splint was a perforated gold alloy attached to the lingual surface of the mandibular incisors.9,10 Pontics were included in later designs, as Howe and Denehy reported in 1977 (Figure 1).11
Figure 1. Zirconia framework in the style of the original cast gold Rochette bridge. (Courtesy of Ian Taylor at Castle Ceramics, Tamworth and clinician Prof Trevor Burke.)
Abutment preparation
The most significant factor in this innovation was that it could be attached to the tooth without any preparation.7,9,10,12 In 1980, however, Livaditis postulated the idea of abutment preparation by way of lingual and proximal reduction to create guide planes and rest seats to increase resistance form for the bridge when replacing a posterior tooth.13 Since then many preparation designs have been proposed, including combinations of grooves, pin holes and ‘wraparound’ tooth reduction (Figure 2).
Figure 2.
(a) Abutment preparation showing 'wraparound' tooth reduction with mesial and distal rest seats. (b) RBB in situ on the working cast. (Courtesy of Ian Taylor at Castle Ceramics.)
It is well documented in the literature that, in certain circumstances, RBBs can be cemented directly to unprepared enamel with disregard to the existing occlusion and, similar to the Dahl principle, the occlusion will correct itself after a short period either by eruption of the molars and/or intrusion of the anteriors (Figure 3).3,4
Figure 3.
(a) No preparation RBB in situ immediately post cementation illustrating disclusion of the posterior teeth. (b) Occlusal view of the RBB. (c) Re-establishment of occlusion following cementation. (Courtesy of Prof Richard Ibbetson which shows how the occlusion has adapted after the anterior bridge was cemented without any abutment preparation.)
Retainers
In 1982, Livaditis and Thompson introduced an electrolytic etching technique using a solution of 3.5% nitric acid with a current of 250mA/cm2 to etch the internal surfaces of the solid base nickel-chromium retainers,7,8,14 thus improving retention micromechanically. It is often referred to as a ‘Maryland Bridge’ as it was pioneered at the University of Maryland, Baltimore, USA.
In 1985, Moons and Hudgins et al created the Virginia bridge which was characterized by particle roughened retainers produced by the ‘lost salt’ crystal technique.7,8
In more recent times, however, wing retainers are most commonly sandblasted (Figure 4).
Figure 4. Typical sandblasted wing retainers. (Courtesy of Ian Taylor at Castle Ceramics.)
Since then little has changed in this formula, except recently with the emergence of a zirconia or EMax framework,15 in an attempt to improve the aesthetics and overcome the commonplace ‘greying’ of the abutment tooth as a result of the metal retainer. Recent studies suggest that a porcelain layer can be added to the retainer wing in a ‘glaze-on’ technique which allows it to be etched; therefore improving its bond strength (Figure 5).16
Figure 5. Porcelain 'glaze-on' technique which can improve the bond strength of zirconia wings. (Courtesy of Ian Taylor at Castle Ceramics.)
The success rates and longevity of RBBs fluctuate from study to study depending on methods used and confounding factors. Historically, failure has been measured as a retainer that has debonded; failure as a result of caries or periodontal disease is often discounted.
Statistics have been published ranging from 92.9% success at 5 years 9 months17 to 57% at 10 years.18
The literature illustrates the controversy and lack of consensus with regards to the overall procedure for the provision of an RBB. It is, however, agreed that resin cements, such as Panavia (Kuraray, Japan), are most effective at cementation as they bond directly to metal and enamel.19 It has also been shown that the weak link in the bond is the enamel-resin interface.20
Tooth preparation
To improve success and attempt to dissipate the stresses within the cement, varying degrees of tooth preparation have been reported. Definite evidence-based guidelines for abutment preparation design do not exist. There are clear descriptions for preparation designs in prosthodontics manuals8,10 but evidence for their effectiveness is vague.
The first suggestion that tooth preparation should be performed to improve retention and resistance was by Simonsen et al; guide planes, axial grooves and cingulum rests were advised.21 Ibbetson2 suggests that, although studies have shown that preparation of abutment teeth can increase retention and resistance form, these studies are mainly in vitro22 and the same results do not translate to in vivo studies.23 He advises that preparation of the palatal surface of upper anterior teeth should be embarked upon tentatively and with consideration to the amount of enamel present, as any amount of preparation could penetrate into dentine, resulting in a decrease in the bond strength of the restoration. This theory was refuted by Olsen, who claimed that enamel reduction had no effect on the shear bond strength and that the incorporation of grooves into tooth preparation designs should not compromise retention (Figure 6).24
Figure 6. Minimal abutment preparation design with just a chamfer finish line. (Courtesy of Ian Taylor at Castle Ceramics.)
Common principles for tooth preparation involve proximal reduction (180° if possible), vertical stops, finish lines and lingual reduction within enamel. Posterior abutments should be prepared similarly but include mesial and distal rest seats.25
Many of the papers refer to a ‘conventional preparation’ which is minimal and in-keeping with the conservative ethos of the RBB. Smith states that the design should endeavour to utilize the maximum surface area of enamel to increase bonding, that it should seat positively and without movement to aid cementation. He advises just a seating ledge on the cingulum of anterior teeth and guide planes, a wraparound design and shallow occlusal rest seats on the marginal ridges for posterior teeth. He explains that, if axial reduction is necessary to increase the thickness of the retainer, then it should be kept in enamel (Figures 7 and 8).26
A literature review was conducted to clarify whether preparation is required for RBBs or if they can be cemented ‘high’. Electronic Medline and manual searches were performed, 20 studies met the inclusion criteria and were reported on (Table 1, Figures 9 and 10).
70% of the studies reviewed were in vivo, of which 36% reported on both fixed-fixed and cantilever bridges, 57% on fixed-fixed only and the remaining 7% not specified. None of the in vivo studies assessed cantilever bridges only.
Only 21% of all in vivo studies were found to have used the same cement throughout. 100% uniformity was found across the samples in in vitro studies; thus making it difficult to assess the reliability of the data reported in the in vivo papers.
Of the six in vitro studies only three; El Salam Shakal et al,27 Aker et al28 and Olsen et al20 tried to replicate oral conditions prior to testing. Two of the in vitro studies involved bonding retainers to metal replica dies.22,29 These results cannot be comparable to bonding to enamel.
Various preparation designs were extracted and common principles found; in general most authors agree that a conventional preparation is more conservative, often including a chamfer finish line, guide planes and possibly a seat rest. In contrast, a modified or ‘extensive’ preparation often exhibited characteristics which included a ‘wraparound’ design, proximal grooves and more definite rests.
70% (14 out of 20) of the studies reviewed concluded that a more extensive preparation resulted in increased success rates for RBBs irrespective of its position: anterior, posterior, maxillary or mandibular.
Creugers et al30 and Boening31 concluded that extensive preparation should be recommended for posterior bridges only and that minimal or no preparation should be advised for anterior bridges.
Boening31 maintains, in his 1996 paper, that a minimal preparation design is adequate for the long-term survival of anterior RBBs. This concurs with the findings of Pjeterssun et al33 in their 2008 systematic review, although neither of these papers comment on posterior RBB design.
Only one of the papers was in complete favour of no preparation (King et al).34 It reported that an increase in tooth preparation led to an increase in failure and that, if the preparation was into dentine, then it was more than twice as likely to fail. The paper does not differentiate between differences in anterior and posterior locations.
Two papers that did support no preparation also advised that minimal (Djemal et al23) or extensive (Creugers et al30) preparations would be of benefit in certain situations, such as in posterior locations.
The paper by Djemal et al23 reviewed splints alongside RBBs (198 out of a total 832 restorations), the outcomes of which were incorporated into the results and could skew the data due to the fact that splints are cemented to multiple teeth and pontics are not included. This may have an impact on their longevity due to the increased risk of debonds occurring at any point across the splint (as a result of independent tooth movement) and that the lack of pontic will decrease the occlusal load.
Rammelsberg et al35 achieved successes of 96% for RBBs with a retentive preparation form consisting of grooves and channels, yet only 37% with a non-retentive preparation. This statistic seems conclusive. However, on closer inspection it was found that multiple operators were used, four different types of metal conditioning were utilized and there was no clear explanation of the number of patients in each cohort who received retentive/less retentive preparations.
Similarly, Barrack and Bretz17 surmised from their investigations that more retentive preparations limit the stresses on the cement and therefore increase the success of RBBs. Their patient cohort included bruxists and the bridges provided ranged from 2 units to 10. The data from this report cannot be compared equally to other more standardized studies and therefore its results are somewhat irrelevant.
Eshleman et al36 conclude that ‘tooth modifications confined to the enamel layer will enhance retention and resistance form of preparations for RBBs and provide space for thicker retainers and connectors.’ Whilst they propose guideline preparation designs for anterior and posterior abutments, they are already biased towards preparation being necessary for the provision of RBBs as there is little information on the benefits of less preparation.
Conclusions
The 20 papers reviewed all had inherent weaknesses in the strength of their findings but, regardless of the confounding factors, the available evidence suggests a more extensive preparation design is more successful, providing it is kept within the boundaries of the enamel.
The principle of cementing an RBB to unprepared enamel and therefore potentially ‘high’ in the occlusion is an accepted form of treatment and, in certain circumstances, can be very successful. However, it is important to consider the findings of Aker et al with regard to the adhesion to enamel prepared with a diamond bur being greater than to unprepared enamel.28
In summary, RBBs can be cemented ‘high’ without any abutment preparation, the benefit being that, if the restoration fails, the abutment teeth have not been irreversibly damaged; the risk being that the restoration will potentially have a shorter longevity.
It has been identified through this review that there is a requirement for randomized controlled trials in this field in order to answer the review's question comprehensively.
This paper was completed as part of the final assessment for the MSc in Advanced General Dental Practice at The University of Birmingham.
